I generally enjoy altering some of the variables in Civilization II's "rules.txt" to give a variety to gameplay. Of particular note is production: to speed up the game a little, I tend to tweak some production values a little higher.
I know that a Railroad will provide certain terrains an additional shield, but I can't seem to find this value anywhere (to potentially bump it up to two shields). Is it configurable somewhere? Or is it simply baked into the game.